Many reactions of commercial importance, including the hydrolysis of esters, are limited by thermodynamic equilibrium, and historical techniques of performing these reactions involved two sequential steps. The first step was the reaction step which ceased when equilibrium was reached. Generally, upon reaching equilibrium, both reactants and products were present in one mixture, therefore necessitating a second step to separate the product of interest from the unconverted reactants which may be recycled to the reactor. The obvious drawbacks to the historical approach are the costs associated with a two-step approach, often involving several reactors and separators, and the equilibrium-imposed limitation on the quantity of product formed.
A technique which has been investigated and applied to equilibrium-limited reactions in order to shift equilibria to favor the yield of products is the use of reactive chromatography. Reactive chromatography has been described as a technique employing a chromatographic and a reactor system that is used both to react components and to concurrently separate one or more of the products that are formed. Several different operating configurations such as a fixed bed with pressure swing or cylindrical annular bed with rotating feed input source, a countercurrent moving bed, and a countercurrent simulated moving bed have been explored. See generally, Vaporciyan, G. G.; Kadlec, R. H. AIChE J. 1987, 33(8), 1334-1343; Fish, B. B.; Carr, R. W. Chem. Eng. Sci. 1989, 44, 1773-1783; and Carr, R. W. In Preparative and Production Scale Chromatography; Ganetsos, G., Barker, P. E., Eds.; Chromatographic Science Series Vol. 61; Marcel Dekker: New York, 1993; Chapter 18.
The hydrolysis of diesters and the concurrent separation of the products has been investigated using a fixed bed chromatographic reactor. See, Sardin, M.; Schweich, D.; Villermaux, J. In Preparative and Production Scale Chromatography; Ganetsos, G., Barker, P. E., Eds.; Chromatographic Science Series Vol. 61; Marcel Dekker: New York, 1993; Chapter 20, pp. 511-516. In this reference, the stated goal of the work was to increase the yield of one of two competing reactions. The chromatographic reactor used in this reference was a column packed with activated charcoal, and the feed contained ethylene glycol diacetate and sodium hydroxide in a carrier of 2.5% ethanol in water. The glycol diacetate reacts with the sodium hydroxide to form glycol monoacetate and sodium acetate and the glycol monoacetate also further reacts with the sodium hydroxide to form glycol and sodium acetate. The stated goal of the experimentation was to increase the yield of the glycol monoacetate; however, this goal was not attained.
Other reactions and separations, such as mesitylene hydrogenation, have been accomplished using simulated moving beds. See, Ray, A.; Tonkovich, A. L.; Aris, R.; Carr R. W. Chem Eng. Sci., 1990, Vol. 45 No. 8, pp 2431-2437. Some applications of simulated moving beds have focused on simultaneous reaction and catalyst regeneration. In U.S. Pat. Nos. 4,028,430 and 4,008,291 an alkylation reaction and catalyst regeneration through the removal of adsorbed water were disclosed. However, applicants are the first to realize that the simulated moving bed technique combined with reactive chromatography can be successfully applied to the hydrolysis of esters to form at least one alcohol and at least one carboxylic acid and specifically applied to the hydrolysis of methyl acetate to form methanol and ethanoic acid. Applying simulated moving bed technology to reactive chromatography for ester hydrolysis will achieve high amounts of conversion with less process equipment as compared to fixed-bed systems. In addition, the disclosed invention eliminates costs associated with the recycle of unconverted reactants which are common in other processes.